Classification of Stainless Steel
There are many types of stainless steel, and we can divide them according to different criteria. According to the organization structure at room temperature, stainless steel can be divided into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, duplex stainless steel and precipitation hardening stainless steel. According to the main chemical composition, it can be divided into chromium stainless steel and chromium-nickel stainless steel. By application, it can be divided into nitric acid-resistant stainless steel, sulfuric acid-resistant stainless steel, seawater corrosion-resisting stainless steel and more. According to the type of corrosion resistance, it can be divided into pitting corrosion-resistant stainless steel, stress corrosion-resistant stainless steel and intergranular corrosion-resistant stainless steel. According to the functional characteristics, it can be divided into non-magnetic stainless steel, easy-cutting stainless steel, low-temperature stainless steel, high strength stainless steel and more.
In this article, we mainly introduce the stainless steel classified according to the organization structure under room temperature conditions.
1.) Austenitic Stainless Steel
Austenitic stainless steel is stainless steel with the austenitic organization (about 18% chromium, 8%-25% nickel, and 0.1% carbon) at room temperature. Austenitic stainless steel is non-magnetic and has high toughness and plasticity, but its strength is low. Generally, it is available to make acid-resistant equipment, such as corrosion-resistant containers, transport pipelines, nitric acid-resistant equipment parts and more. In addition, it can also be used as the main material of stainless-steel watch jewelry.
2.) Ferritic Stainless Steel
Ferritic stainless steel containing chromium in the range of 15%-30%, with a body-centered cubic crystal structure. This type of stainless steel generally does not contain nickel, and sometimes there is a small amount of molybdenum, titanium, niobium and other elements, with good oxidation resistance, corrosion resistance and resistance to chloride corrosion rupture. Ferritic stainless steel, according to the content of chromium, can be divided into three categories: low chromium, medium chromium and high chromium. According to the purity of the steel, especially carbon, nitrogen impurity content, it can be divided into plain ferritic stainless steel and ultra-pure ferritic stainless steel.
3.) Martensitic Stainless Steel
Martensitic stainless steel is low-carbon stainless steel manufactured according to type 410 steel (consisting of iron, 12% chromium and 0.12% carbon), mainly used for steam turbine blades, cutlery and surgical instruments. According to the difference in chemical composition, it can be divided into two categories: martensitic chromium steel and martensitic nickel-chromium steel; according to the difference in the organization and strengthening mechanism, it can be divided into martensitic stainless steel, martensitic and semi-austenitic precipitation hardening stainless steel and maraging stainless steel.
4.) Duplex Stainless Steel
Duplex stainless steel is stainless steel with 50% ferritic and 50% austenitic. This type of stainless steel has both austenitic and ferritic stainless-steel characteristics. Compared with ferritic, duplex stainless steel has higher plasticity, toughness, intergranular corrosion resistance and weldability, while also maintaining the ferritic stainless-steel characteristics of 475 ℃ brittleness and high thermal conductivity. Compared with austenitic stainless steel, it has high strength and significantly improves the resistance to intergranular corrosion and chloride stress corrosion.
5.) Precipitation Hardening Stainless Steel
Precipitation hardening stainless steel is to add hardening elements in various types of stainless steel to obtain the features of high strength, high toughness and high corrosion resistance, which is widely used in cutting-edge industry and civil industry. According to its matrix metallographic organization, it can be divided into martensitic precipitation hardening stainless steel(17-4PH), semi-austenitic precipitation hardening stainless steel (AM-355 stainless steel), and austenitic precipitation hardening stainless steel three categories.